Advice on Mammoth CNC Router Build - Steel Framed - 2440mm x 1220mm cutting area!

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Originally Posted by Wejjmeister

expand on the disadvantages??

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If the rails are on the bottom surface then the bearings, i.e. your supporting points, are closer to the tool/bed. The overhang is therefore reduced, so the stiffness is correspondingly higher. It does however make mounting them on epoxy more challenging - although you could conceivably mount the Y rails and X bearing blocks on the same epoxy leveled surface and get very good accuracy. I'd try drawing both orientations and see which looks the most promising.

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Originally Posted by Lee Roberts

Surly enough accuracy can be achieved when cutting and then wielding the frame that any small differences would be "levelled" out from doing an epoxy bed for the rails to then sit on?

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I tend to agree - there becomes a point when an extra couple of mm of epoxy doesn't cost much compared to the added material/time required to get the frame more accurate. The epoxy is pretty strong/hard and the damping properties may be useful, so I wouldn't be too concerned about minimizing the thickness, within reason. If you look in my build log the epoxy is quite thick, but don't treat that build log as gospel - there's plenty of room for improvement.

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Originally Posted by EddyCurrent

That's the method I'm also using and I found that after welding, one corner of the frame was 3mm out of level with the other. This might be regarded as too much depth for epoxy treatment alone. I don't know for sure ? but at least I can shim the rails to as near level as possible then use epoxy from there.

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Thanks Eddy, any idea why this happened or?

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Originally Posted by Clive S

Eddy You might have seen this before there is no problem with the thickness of the epoxy Jonathan and I have used it I think Dean uses some sort of epoxy putty which is stiffer, he has explained that on other threads.

I poured this to about 5mm deep it is very slow setting 10 - 20 hours and don't touch it for 48 hours. Wests system
..Clive

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Hi Clive, in your picture to make your epoxy "gutters" you look to have used MDF, i dont know if you've seen Jonathan's recent machine but he made his using aluminum and then left those in place once the machine was ready. My question is, what are the edges like on the epoxy once it "sets", i.e dose it need protecting from damage and so on to keep it together.

Did you do anything to yours after the machine was ready to be used to keep it safe?

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Originally Posted by Jonathan

I tend to agree - there becomes a point when an extra couple of mm of epoxy doesn't cost much compared to the added material/time required to get the frame more accurate. The epoxy is pretty strong/hard and the damping properties may be useful, so I wouldn't be too concerned about minimizing the thickness, within reason. If you look in my build log the epoxy is quite thick, but don't treat that build log as gospel - there's plenty of room for improvement.

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Thanks JB, I didnt see your post untill i posted mine.

.Me

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Hi Clive, in your picture to make your epoxy "gutters" you look to have used MDF, i dont know if you've seen Jonathan's recent machine but he made his using aluminum and then left those in place once the machine was ready. My question is, what are the edges like on the epoxy once it "sets", i.e dose it need protecting from damage and so on to keep it together.

Did you do anything to yours after the machine was ready to be used to keep it safe?

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It is 10mm MDF the box section is 60x60 the MDF is placed right on the edge (just on the round part of the box) and then a very thin bead of silicone was run around the inside of the moat to stop any leaks. I also rubbed a little oil on my finger and ran that around to stop the epoxy sticking to the MDF.

The epoxy is like water and runs around ok. When it was cured the MDF was removed (the epoxy creaps up the inside of the MDF a little) Then I used a scraper and a flat file to get rid of the edges that were raised, it is easy to see when you are scraping it because it will start marking the centre.

The rails were then screwed right through the epoxy into the steel. Job done. The epoxy can be chamfered off at the edges as it can be very sharp like glass. ..Clive

I've used both methods in the past and each work good and each have there own +/-

Full Epoxy level is ok and works good but has you can see with clives pictures there's plenty of prepartion required and on large machine like what the OP wants this means a lot of work. This prep has to be very good and fully sealed other wise sag can happen and being 3mtr length the chances of this happening are plenty.
Yes it's not the end of the world and can be corrected if it happens but it's a ball ache when it happens.!! . . . . I'm sure Both clive and Jonathan will tell you when pouring and it starts leaking your running round like headless chicken trying to suppress it and again over 3mtr and between 80-100mm width that's a fair amount of epoxy your fighting with.! . . . . It's also not cheap.

Now with Epoxy putty feet and shims you don't have this problem has there's no liquid epoxy involved but you do still have to do careful measuring and setting up to get rails on same plane. Unlike The above epoxy method which takes care of this for you, thou if it's not perfect which you won't really findout until machine is built and working then it's a lot more work to correct.
The epoxy shimming is very easy to correct on the fly and while machine complete and working. You don't need to strip it down to correct.

Now to be honest I think the OP is correct to use Both methods has 3mtr is a long length of boxsection to ensure is straight and true, which it won't be, so would need some work even with Epoxy putty method and the Epoxy liquid method will make light work of this. The Epoxy putty and Shims will give him the fine tuning he will need over this length machine.!!

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Originally Posted by Clive S

It is 10mm MDF the box section is 60x60 the MDF is placed right on the edge (just on the round part of the box) and then a very thin bead of silicone was run around the inside of the moat to stop any leaks. I also rubbed a little oil on my finger and ran that around to stop the epoxy sticking to the MDF.

The epoxy is like water and runs around ok. When it was cured the MDF was removed (the epoxy creaps up the inside of the MDF a little) Then I used a scraper and a flat file to get rid of the edges that were raised, it is easy to see when you are scraping it because it will start marking the centre.

The rails were then screwed right through the epoxy into the steel. Job done. The epoxy can be chamfered off at the edges as it can be very sharp like glass. ..Clive

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Thanks Clive, I liked the tip on silicone, will add that to the mental archive for when the time comes. Good idea on the chamfering, i was thinking about what i could use to protect it once done but it sounds like its quite durable.

Clive, where is your build log?

.Me

That's the method I'm also using and I found that after welding, one corner of the frame was 3mm out of level with the other.

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Originally Posted by Lee Roberts

Thanks Eddy, any idea why this happened or?

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Because I assumed my garage floor was level and I just built it from that datum.

Attachment 11219Attachment 11220

First stage of the MkII done, Im still working on it so bear with me. I decided just to use the epoxy on the tops of the rails as plates and shims plus epoxy will be a mare. It may be slightly better but I dont intend on moving it once set up so I think Epoxy should suffice.

The whole of the frame will be sand filled too, so not worried about resonance.

Next step is the rails and ballscrews and placements of. Will add more a little later hopefully, time permitting!

Thanks ever so much for all of the comments though guys, a real help!

The diagonals at the sides, it seems to me help nothing except add weight. Should work fine without them, but that's me :-)

Looks ok... but probably a bit OTT. Don't leave the ends of the long pieces of box section cantilevered - support them with a piece at 45°.

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Originally Posted by JAZZCNC

I'm sure Both clive and Jonathan will tell you when pouring and it starts leaking your running round like headless chicken trying to suppress it

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I've not had any leaks at all. The guiding aluminium strips were firmly bolted to the frame, and the wooden pieces used covered with grease, which makes a good seal, and clamped with plenty of G-clamps. If it had leaked then I would have addressed the situation in a calm manner, using the glue gun and tape I had on hand just in case. The running round can be left to the three birds in the garden...

Sorry for interrupting but I have an idea
Could it be possible to combine both methods (epoxy and shims) BUT instead of epoxy use clear coat for car painting. The clear coat will be the mean to show us which is the true level between the rails, so then we put shims and putty and fit the rails on that level. For that size of machine that may be 2-3 kgr of epoxy will be needed, the difference to the final cost will be significant After the putty pures we could even took off the clear coat as I don’t know how strong it is in getting pressure from the rails. In that way we don’t pay too much money for the epoxy as I think clear coat is much cheaper and we won’t waste too much time to true level the rails as we use the clear coat as guide. Regards the pure time of clear coat we could use a catalyst that will make pure time longer.
Also instead of clear coat we could use anything chaper that has self leveling properties
Just an idea I don’t know if it is correct

Vagelis